1. Field of the Invention
The present invention relates generally to modems and, more particularly, to the use of a digital isolation barrier as a digital communication bus between a modem and a host.
2. Related Art
As in other computer-related areas of technology, the modem technology has been on a rapid pace of change and progress, and has evolved tremendously since about just two decades ago. Modem (or Modulator/Demodulator) is a device that adapts a host, such as a terminal or computer to a communication medium, such as an analog telephone line, by converting digital pulses to audio frequencies and vice versa. The term modem also refers to and encompasses cable or DSL modem or ISDN terminal adapter for purposes of the present invention. Also, for purposes of the present invention, a host includes any information handling system, such as a computer, set-top box, game console or any other device or system that utilizes the modem to communicate via the communication medium.
FIG. 1A provides a glance at the modem evolution throughout the recent years. As shown, in one conventional embodiment, modem 100 communicates data with host 101, such as a terminal or a computer, in digital format, via modem side bus interface 104. As shown, host 101 includes host bus/connector 103, which provides a connection between host 101 and modem 100 via host side bus interface 102 and modem side bus interface 104. Modem 100 is further capable of communicating with a remote device, in analog format, via telephone network 108. Telephone network 108 may be part of a public switched telephone network (“PSTN”). It should be noted that, throughout the present application the terms “bus” and “connector”, may be used interchangeably, and either term refers to any type of conductor or channel that is capable of providing a communication path.
Modem 100 depicts an early modem design, which is known as a controller-based modem. As shown, modem 100 includes controller 105, digital signal processor (“DSP”) 106 and data access arrangement (“DAA”) 107. In such design, controller 105 controls all the modem functions and modem components, including DSP 106 and DAA 107. Controller 105 also controls modem side bus interface 104. Controller can be any type of microprocessor, such as a Rockwell 6502-based processor. Controller 105 executes instructions residing in a memory device (not shown), such as an EPROM, which stores the modem software. According to the instructions stored in the memory, controller 105 is able to control DSP 106, DAA 107 and modem side bus interface 104. DSP 106 performs the task of modulating signals received via modem side bus interface 104 and transmitting the modulated signals to DAA 107 for digital to analog conversion and transmission over the telephone line. Further, DSP 106 demodulates signals received from DAA 107 after analog to digital conversion by DAA 107 and provides the demodulated signals for transmission over modem side bus interface 104 to host 101.
DAA 107 generally refers to circuitry, which provides an interface with a telephone line originating from the telephone central office. DAA 107 electrically isolates the rest of modem 100 from the telephone line. For example, DAA 107 provides galvanic isolation to prevent voltage surges or transients originating from modem 100 from having a deleterious effect on telephone network 108. Electrical isolation also addresses potential problems associated with differences in operating voltages between the telephone line and modem 100. More particularly, telephone line voltages may vary widely across a given network, and often exceed the operating voltage of modem 100. In addition to electrical isolation, DAA 107 often provides a variety of signals, such as a ring signal for use by modem 100.
As a next generation of modems, controllerless modem 110 was introduced, which includes modem side bus interface 114, DSP 116 and DAA 117, but not a controller, for use to enable host 111 to communicate over telephone network 118. In such designs, a host controller (not shown) residing in host 111 controls controllerless modem 110 via host side bus interface 112, which may be connected to modem side bus interface 114 via host bus 113. DSP 116 and DAA 117 perform similar functions as DSP 106 and DAA 107, respectively.
Turning to a more recent generation of modems, soft modem 120 includes DAA 127, but neither a controller nor a DSP, for use to enable host 121 to communicate over telephone network 128. According to the soft modem design, a host controller (not shown) residing in host 121 provides DSP functionality and further controls soft modem 120 via host side bus interface 122, which may be connected to modem side bus interface 124 via host bus 123. DAA 127 performs similar functions as DAA 107 and DAA 117.
Such existing modem configurations, however, introduce many drawbacks, inefficiencies and excessive costs when such modems are submitted for homologation or approval by regulatory agencies throughout the world, which have established standards and regulations in each country, for connecting subscriber equipment, such as a modem to a telephone network. The homologation procedures are intended to confirm compliance with telephone standards and regulations in each country in order to prevent damage to the telephone network and mitigate interference with other equipment also connected to the telephone network. The homologation procedures, however, often present difficult design challenges, can be lengthy and result in excessive costs to be incurred by applicants. For example, worldwide homologation typically takes between 6-12 months and can cost in the range of $100,000 to $200,000. Accordingly, modem homologation is a main source of costs, delays and engineering burden that must be endured by modem manufacturers for each new modem design.
Turning to FIG. 1B, it illustrates an evolutionary block diagram of various conventional host or computer connectors/buses for modem communications. Originally, desktop computers provided a serial interface, such as an RS-232 serial bus (Recommended Standard by TIA/EIA) 130, which later evolved into universal serial bus (“USB”). RS-232 serial bus 130 uses a 25-pin DB-25 or 9-pin DB-9 connector. Next, the Industry Standard Architecture (“ISA”) bus 131 was introduced in various form factors to function as an expansion bus commonly used in personal computers. ISA bus 131 can accept plug-in boards that control peripheral devices, such as modems. As a later generation of personal computer buses, Peripheral Component Interconnect (“PCI”) bus 132 was introduced, as a peripheral bus commonly used in personal computers. PCI bus 132 provides a high-speed data path between the host processor and peripheral devices, such as modem devices. There are typically three or four PCI slots on a given motherboard.
A more recent personal computer bus is Audio/Modem Riser (“AMR”) bus 133 that supports a plug-in card into the motherboard that contains audio and/or modem circuits. AMR bus is a 46-pin bus that provides the digital interface between the card and the motherboard. AMR bus has evolved into a Communications and Networking Riser (“CNR”) bus with a 30-pin interface and an Advanced Communications Riser (“ACR”) bus with a 106-pin interface. CNR and ACR provide additional support, such as LAN, DSL or Ethernet interface.
Similar personal computer buses have been introduced for laptop computers, such as ISA bus 140 with proprietary interfaces, Personal Computer Memory Card International Association (“PCMCIA”) bus 141, Mini PCI bus 142, similar to PCI bus 122, and Mobile Daughter Card bus (“MDD”) 143, similar to AMR bus 133.
Existing personal computer buses for modem communications, however, suffer from many problems, such as too many connector pins, occupying too much space, and not being uniform in pin-outs and specifications. As a result, various modem side bus interfaces (such as modem side bus interfaces 103, 113 and 123) must be provided for each modem design for compliance with numerous bus standards. Therefore, excessive costs must be incurred and many hours of engineering efforts must be spent to design and manufacture modems with various modem side bus interfaces.
Furthermore, in the more recent years, as soft modems continue to displace traditional hardware modems, such as modem 100 and modem 110, silicon DAAs have, as a result, been experiencing rapid growth. As discussed above, DAAs are used as telephone line interfaces and are required in any device that connects to the telephone line or any other similar communication line. Traditionally, DAAs have been implemented in analog modems, such as modem 100, as an assortment of transformers, relays, opto-isolators and discrete components. But, in order to reduce the high cost, power consumption and space associated with the traditional DAAs, DAAs started to be designed for silicon implementation, thus giving rise to silicon DAAs. Early on, silicon DAAs relied on the transfer of analog signals across an isolation barrier and still required many discrete components. Lately, however, silicon DAA solutions utilize an integrated codec and transmit digital signals across capacitors to reduce cost, power consumption and space. For example, FIG. 1 of the commonly-assigned U.S. Pat. No. 6,351,530, issued Feb. 26, 2002, which is incorporated by reference in the present patent application, illustrates an exemplary silicon DAA design. The DAA includes a digital isolation barrier coupled to a system side circuitry at one end and to a line side circuitry at the other. Line side circuitry includes a digital isolation barrier interface and a codec, and is connected to a telephone line. Also, the system side circuitry includes a digital isolation barrier interface and a host interface, and is connected to a host via a connector.
Today's silicon DAA solutions, however, still fail to insulate host side components and the DAA. Therefore, clearance and creepage of DAA components and other components must still be addressed during the design process, which require expert knowledge and cause additional costs and time to market delays. In addition, each new design including the DAA and the host side components, in combination, must be formally tested in accordance with the safety requirements and regulatory homologation regulations. Accordingly, a given silicon DAA must undergo the homologation process, in combination with the system in which the silicon DAA has been designed into, over and over again, which, as stated above, causes a delay of about 6-9 months and costs of about $100,000-$200,000, for worldwide homologation.